Safety device



,1. H. HAMMOND, JR 1,

SAFETY DEVICE Filed July 12, 1926 Sept. 9, 1930. Q

' Inventor: v

John-H.r1ammond JR,

' Hls Attorney.

Patented Sept. 9, 1930 PATENT OFFICE JOHN HAYS HAMMOND, TIL, F GLOUCESTER, MASSACHUSETTS I SAFETY Application filed July 12,

My present invention relates to filament safety-devices.

his one of the objects of my invention to provide a" simple, inexpensive and reliable means for preventing the operation of the filaments of electron discharge devices above their rated voltage.

In the operation of electron discharge devices, the voltage sup lied to the filaments is frequently increased eyond the rated voltage with the result that the filaments may be burned out and the discharge devices rendered useless. According to the present invention, when the voltage supplied to a filament reaches a predetermined amount, further -increase of the voltage is automatically prevented.

The novel features which I believe to be characteristicof my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation will best be understood by reference to the following specification taken in connection with the accompanying drawing in which Fig. 1 is a rear perspective view of a control device embodying the features of my invention; Fig. 2 is a front elevation of the'control panel shown in Fig. 1, while Fig. 3 is a diagrammatic view of the electrical connections and ap aratus shown in Fig. 1.

eferring to the drawing, I have indicated at 1 and 2 a pair of resistors mounted on a r0- tatable insulating drum 3 which is provided with a ratchet 1 arranged intermediate the resistors and adapted to cooperate with a locking pawl 5. A pair of stationary contact fingersfi and 7 engage the resistors 1 and 2 to control the voltage supplied respectively to the filament of an electron discharge device or load 8 and to an electromagnet or relay 9. A circuit, comprising resistor 1 and the filament of the discharge device 8, is connected in parallel. with a circuit comprising resistor 2 and relay 9; both circuits being connected to a source of energy indicated at 10.

Pawl 5 is held out of engagement with the ratchet 4 by means of a catch 11 mounted on a shaft 11' which is adapted to be actuated by DEVICE 1926. Serial 1W0. 121,892.

means of the ivoted armature 13 of electromagnet 9. T e locking pawl 5 is provided on the upper end thereof with a relatively long insulating portion 14 and a relatively short conducting portion 15, the latter portion being adapted to be engaged by catch 11 when the pawl is held in its non-locking or elevated position.

If pawl 5 is in engagement with ratchet 4; and it is desired to supply current to the filament of the discharge device 8, a knob 16 mounted on a shaft 12 is actuated in a direction to increase the amount of resistance in circuit with the winding of electromagnet 9 and with the filament of the discharge device 8. When the resistance is practically all in circuit, a cam 17 on the ratchet 4 rotates pawl 5 against the action of a spring 18 and allows catch 11 to engage the conducting part 15 of the pawl. Drum 3 may now be rotated in the opposite direction to complete a circuit from the positive pole of the source of energy 10, through the resistor 2, pawl 5, part 15 and relay 9 to the negative pole of the source of energy. A second circuit is at the same time completed from the positive pole of the source through resistor 1 and the filament of discharge device 8 to the negative pole. Relay 9 will thus be energized and tend to raise its armature 13 and rotate shaft 11. This action, however, is opposed by a spring 19 which may be adjusted, by means of a set screw 20 anda tensioning device 21, to hold the armature in its lower or inoperative position until thevoltage supplied to the relay reaches a predetermined amount. p

A voltmeter 22 is connected across the filament terminals, and mounted on a panel 23, as indicated in Fig. 2. If the resistance of the filament of the discharge device 8 and its parallel connected voltmeter are taken as R1, and the resistance of relay 9 as R2, and the portions of resistors 1 and 2 which may be included in circuit at any time as R3 and R4.- respectively, then the values of R1 and R2 R1 R3 should be so proportioned that In this manner, when a certain voltage exists across the filament of dischargedevice 8, the

same voltage will exist across the relay 9 and 00 'dischar e device.

this relation will exist at all battery voltages. To initially adjust the apparatus, knob 16 is turned until the volt-meter 22 indicates the correct voltage to be'applied to the filament of the device 8 and at this point relay 9is adjusted to actuate its pivoted armature to release the locking pawl 5 and thereby prevent further movement of the resistor to increase the voltage across the filament of the Thereafter in the movement 0 resistors 1 and 2 to supply current to the filament of the discharge device, pawl 5 will be automatically released when the voltage across the filament reaches the point determined int-he preliminary adjustment and further forward movement of the resistor to increase the voltage of the filament will be prevented. In order to reset pawl 5 the knob 16 must be turned back to zero at which point the cam 17 will raise pawl 5 until catch 11 reengages it. The resistor can then be again operated to supply current to the filament. When the relay 9 releases the pawl the circuit through the relay is automatically opened by the insulated portion 14. No power will therefore be consumed by the relay 9 except during the preliminary adjustment of the resistors and consequently little power is required in the operation of the apparatus mainly for demonstration set-ups. Ordinarily it is unnecessary and would be omitted. What I claim as new and desire to secure by Letters Patent of the United States is 1. In combination, a circuit including a rheostat and a device to be controlled thereby, means for supplying current to said device and rheostat, said rheostat comprising a movable member, locking means adapted to prevent movement of said member in one direction, said locking means being normally in an inoperative position but automatically operable when the voltage across said device,

rises to a predetermined value to engage said movable member and to prevent movement of said member to decrease the resistance in cir-.

cuit-with said device until said resistance has been increased. l

2. In combination, a circuit including a rheostat and a device to be controlled thereby, means whereby current may be supplied to said device and rheostat, said rheostat comprising a movable member, locking means for controlling the movement of said member in one direction, means including an electro- 1nagnet for controlling said locking means,

member and prevent decrease of the resistance in said circuit until said resistance has been increased. I

'3. In combination, a circuit including a rheostat and a device to be controlled thereby, a second circuit connected in parallel with said first circuit, the second circuit including a normally energized electromagnet, means controlled by the electromagnet for preventing movement of said rheostat'to decrease the resistance in circuit with said device, said means being automatically operable when the voltage across said device reaches a predetermined value.

4. In combination, a circuit includin a rheostat and a device to be controlled there y, locking means associated with the rheostat and adapted to prevent movement of the rheo-' stat to decrease the resistance in circuit with said device, a second circuit connected in parallel with the first mentioned'circuit, said second circuit including an electromagnet, and means controlled by said electromagnet for operating said locking means and for across said device equals a predetermined amount.

5. In combination, a pair of resistors, one 7 of said resistors being connected to an electromagnet, and the other of said resistors being adapted to be connected to a device to be cont-rolled thereby, means for simultaneously varying said resistors, locking means associted with the resistors and adapted to prevent a decrease in the resistance in circuit with said means to be controlled, and means controlled by said electromagnet for automatically operating said locking means and for opening the circuit of the electromagnet when the voltage across the device to be controlledreaches a predetermined amount.

6. In combination, an insulating drum, 8.

pair of resistors mounted thereon and ada ted to cont-r01 the supply of current to a ura'lity of devices, a ratchet wheel mounte on said drum, a pawl adapted to engage the ratchet and thereby prevent movement of the resistors in one direction, means for holding the pawl out of engagement with the ratchet, and means including a cam surface on said ratchet wheel for actuating said pawl to an inoperative position when the greater part of said resistors is included in circuit with said devices. 7

7 In combination, a rheostat adapted to be connected to a load to control the current supplied thereto, said rheostat includin a movable element, a locking'device contro ling the movable element, and means including an 95 opening said second circuit when the voltage electromagnet for controlling the operation of the locking device, the electroma et and load being connected in circuit in sue a manner that the voltage across said electromagnet is at all times substantially equal to the voltage across the load.

8. In combination, an insulating drum, a resistor mounted thereon and ada ted to control the supply of current to a device, a ratchet wheel mounted on said drum, a pawl adapted to engage the ratchet and thereby prevent movement of the resistor in one direction, means for holding the pawl out of en-- gagement with the ratchet, and means ineluding a cam surface on said ratchet wheel for actuating said pawl to an inoperative position with respect to said drum.

In witness whereof, I have hereunto set my hand this second day of July, 1926. JOHN HAYS HAMMOND, JR. 

